Showing papers by "Kazuhiko Maeda published in 2016"
TL;DR: The results of photocatalytic reactions, emission decay measurements, and time-resolved infrared spectroscopy indicated that Ag nanoparticles on C3N4 collected electrons having lifetimes of several milliseconds from the conduction band of C2N4, which were transferred to the excited state of RuRu', thereby promoting photocatalyst CO2 reduction driven by two-step photoexcitation of C3n4 and RuRu'.
Abstract: A metal-free organic semiconductor of mesoporous graphitic carbon nitride (C3N4) coupled with a Ru(II) binuclear complex (RuRu′) containing photosensitizer and catalytic units selectively reduced CO2 into HCOOH under visible light (λ > 400 nm) in the presence of a suitable electron donor with high durability, even in aqueous solution. Modification of C3N4 with Ag nanoparticles resulted in a RuRu′/Ag/C3N4 photocatalyst that exhibited a very high turnover number (>33000 with respect to the amount of RuRu′), while maintaining high selectivity for HCOOH production (87–99%). This turnover number was 30 times greater than that reported previously using C3N4 modified with a mononuclear Ru(II) complex, and by far the highest among the metal-complex/semiconductor hybrid systems reported to date. The results of photocatalytic reactions, emission decay measurements, and time-resolved infrared spectroscopy indicated that Ag nanoparticles on C3N4 collected electrons having lifetimes of several milliseconds from the co...
365 citations
TL;DR: A photoelectrochemical cell comprising a NiO-RuRe photocathode and a CoOx/TaON photoanode showed activity for visible-light-driven CO2 reduction using water as a reductant to generate CO and O2, with the assistance of an external electrical and chemical bias produced by a pH difference.
Abstract: Photoelectrochemical CO2 reduction activity of a hybrid photocathode, based on a Ru(II)–Re(I) supramolecular metal complex photocatalyst immobilized on a NiO electrode (NiO–RuRe), was confirmed in an aqueous electrolyte solution. Under half-reaction conditions, the NiO–RuRe photocathode generated CO with high selectivity, and its turnover number for CO formation reached 32 based on the amount of immobilized RuRe. A photoelectrochemical cell comprising a NiO–RuRe photocathode and a CoOx/TaON photoanode showed activity for visible-light-driven CO2 reduction using water as a reductant to generate CO and O2, with the assistance of an external electrical (0.3 V) and chemical (0.10 V) bias produced by a pH difference. This is the first example of a molecular and semiconductor photocatalyst hybrid-constructed photoelectrochemical cell for visible-light-driven CO2 reduction using water as a reductant.
236 citations
TL;DR: In this article, the reaction of water splitting using a semiconductor photocatalyst with sunlight has been studied as a potential means of large-scale H2 production from renewable resources.
Abstract: Overall water splitting using a semiconductor photocatalyst with sunlight has long been viewed as a potential means of large-scale H2 production from renewable resources. In general, the reaction c...
141 citations
TL;DR: This study demonstrated the first successful example of an energy conversion scheme using carbon nitride through photocatalytic CO2 reduction, and polymeric Ru species, which were formed in situ from RuCP on C3N4 under irradiation in a solvent having a high donor number, were active catalysts for CO formation.
Abstract: Photocatalytic CO2 reduction using hybrids of carbon nitride (C3N4) and a Ru(II) complex under visible light was studied with respect to reaction solvent. Three different Ru(II) complexes, trans(Cl)-[Ru(X2bpy) (CO)2Cl2] (X2bpy = 2,2′-bipyridine with substituents X in the 4-positions, X = COOH, PO3H2, or CH2PO3H2), were employed as promoters and will be abbreviated as RuC (X = COOH), RuP (X = PO3H2), and RuCP (X = CH2PO3H2). When C3N4 modified with a larger amount of RuCP (>7.8 μmol g–1) was employed as a photocatalyst in a solvent having a relatively high donor number (e.g., N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO)) with the aid of triethanolamine (TEOA) as an electron donor, the hybrid photocatalyst exhibited high performance for CO2 reduction, producing CO and HCOOH with relatively high CO selectivity (40–70%). On the other hand, HCOOH was the major product when RuC/C3N4 or RuP/C3N4 was employed regardless of the loading amount of the Ru(II) complex and the...
110 citations
TL;DR: A hybrid photocatalytic system consisting of a Ru(ii) binuclear complex and Ag-loaded TaON can reduce CO2 to HCOOH by visible light irradiation even in aqueous solution.
Abstract: A hybrid photocatalyst consisting of a Ru(II) binuclear complex and a Ag-loaded TaON reduced CO2 by visible light even in aqueous solution. The distribution of the reduction products was strongly affected by the pH of the reaction solution. HCOOH was selectively produced in neutral conditions, whereas the formation of HCOOH competed with H2 evolution in acidic conditions. Detailed mechanistic studies revealed that the photocatalytic CO2 reduction proceeded via ‘Z-schematic’ electron transfer with step-by-step photoexcitation of TaON and the photosensitizer unit in the Ru(II) binuclear complex. The maximum turnover number for HCOOH formation was 750 based on the Ru(II) binuclear complex under visible-light irradiation, and the optimum external quantum efficiency of the HCOOH formation was 0.48% using 400 nm monochromic light with ethylenediaminetetraacetic acid disodium salt as a sacrificial reductant. Even in aqueous solution, the hybrid could also convert visible-light energy into chemical energy (ΔG0 = +83 kJ mol−1) by the reduction of CO2 to HCOOH with methanol oxidation.
80 citations
TL;DR: To the best of the knowledge, this system constitutes the first example that a particulate photocatalytic material that is capable of water oxidation upon excitation by visible light can also operate at such long wavelengths, even when it is based on earth-abundant elements only.
Abstract: Cobalt-based compounds, such as cobalt(II) hydroxide, are known to be good catalysts for water oxidation. Herein, we report that such cobalt species can also activate wide-band-gap semiconductors towards visible-light water oxidation. Rutile TiO2 powder, a well-known wide-band-gap semiconductor, was capable of harvesting visible light with wavelengths of up to 850 nm, and thus catalyzed water oxidation to produce molecular oxygen, when decorated with cobalt(II) hydroxide nanoclusters. To the best of our knowledge, this system constitutes the first example that a particulate photocatalytic material that is capable of water oxidation upon excitation by visible light can also operate at such long wavelengths, even when it is based on earth-abundant elements only.
74 citations
TL;DR: In this paper, the authors showed that in an aqueous solution, [Ru(dmb)2−(BL)−Re(CO)3Cl]2+ (BL = bridging ligand) most efficiently photocatalyzed the reduction of CO2 to CO under visible-light irradiation using 2-(1,3-dimethyl-2,3dihydro-1H-benzimidazol-2-yl)benzoic acid (BI(CO2H)H) as a water-soluble sacrificial redu
70 citations
TL;DR: An yttrium-tantalum oxynitride having a band gap of 2.1 eV was applicable as a semiconductor component of a Z-scheme CO2 reduction system operable under visible light, in combination with a binuclear Ru(ii) complex that has strong absorption in the visible region (<600 nm).
48 citations
TL;DR: In this article, a C3N4 powder modified with a catalytic Ru(II) complex having carboxylic acid groups as anchors showed higher activity for CO2 reduction into HCOOH under visible light (λ > 400 nm).
Abstract: Semiconducting C3N4 powder modified with a catalytic Ru(II) complex having carboxylic acid groups as anchors showed higher activity for CO2 reduction into HCOOH under visible light (λ > 400 nm) at ...
41 citations
TL;DR: Dual- functional photocatalysis for H2 evolution with the simultaneous mineralization of 4-chlorophenol was achieved under de-aerated conditions using a Cr2O3/Rh/SrTiO3 photocatalyst which has Rh nanoparticles covered with a thin Cr2 O3 barrier layer to selectively control and maximize the dual-functional photocatalytic activity.
36 citations
TL;DR: This work attempted to synthesize heterojunctioned nanoparticles consisting of a transition metal and Cr on powdered SrTiO3, an n-type semiconductor exhibiting photocatalytic activity for overall water splitting, and found that increasing the proportion of Cr was found to suppress the reverse reaction (that is, H2-O2 recombination).
Abstract: This work attempted to synthesize heterojunctioned nanoparticles consisting of a transition metal and Cr on powdered SrTiO3, an n-type semiconductor exhibiting photocatalytic activity for overall water splitting. This was performed via band gap irradiation of SrTiO3 (λ > 300 nm) in an aqueous methanol solution containing a transition metal precursor and K2CrO4. The resulting multicomponent nanoparticles were examined as promoters for photocatalytic overall water splitting. Among the transition metals examined, Au and Pd became effective promoters for overall water splitting upon codeposition of Cr. In the case of Au, which is stable in its metallic state, the resulting (Au+Cr) nanoparticles had a core/shell structure consisting of metallic Au (the core) and amorphous Cr2O3 (the shell), similar to Au/Cr2O3 prepared by a stepwise photodeposition method. However, when using a core transition metal with a tendency to form an oxide, such as Pd, the nanoparticles had different morphologies and electronic states...
TL;DR: Experimental results demonstrated that the reduction of IO3 (-) is the rate-limiting step in this reaction and that nanosheets with less distorted structures are advantageous with regard to increasing both light absorption and the mobility of photoexcited charge carriers.
Abstract: Metal oxide nanosheets having a three-layer perovskite structure were studied as photocatalysts for water oxidation in the presence of IO3 (-) as a reversible electron acceptor. This work examined the effects of the lateral dimensions and composition of the nanosheets as well as metal oxide co-catalysts deposited on the restacked nanosheets. Depositing metal oxides capable of promoting reduction reactions on the nanosheets were found to promote the water oxidation activity. In contrast, the lateral dimensions and the degree of crystallinity of the nanosheets had little effect on the activity. Experimental results demonstrated that the reduction of IO3 (-) is the rate-limiting step in this reaction and that nanosheets with less distorted structures are advantageous with regard to increasing both light absorption and the mobility of photoexcited charge carriers.
TL;DR: In this paper, the photocatalytic activity of the Dion-Jacobson perovskite Ca2Nb2TaO10− with tetra-n-butylammonium hydroxide (TBA+OH−) was investigated.
TL;DR: In this article, the reaction of water splitting using a semiconductor photocatalyst with sunlight has been studied as a potential means of large-scale H2 production from renewable resources.
Abstract: Overall water splitting using a semiconductor photocatalyst with sunlight has long been viewed as a potential means of large-scale H2 production from renewable resources. In general, the reaction c...
01 Jul 2016
TL;DR: Amorphous Fe(III)-Cr(III) mixed oxide nanoparticles were deposited on the surface of powdered SrTiO3 from an aqueous solution containing FeCl3 and K2CrO4, using a photochemical method and without the aid of a heat treatment as discussed by the authors.
Abstract: Amorphous Fe(III)–Cr(III) mixed oxide nanoparticles were deposited on the surface of powdered SrTiO3 from an aqueous solution containing FeCl3 and K2CrO4, using a photochemical method and without the aid of a heat treatment. The mixed oxide was found to function as a cocatalyst for water oxidation.
17 Mar 2016
TL;DR: In this article, the authors describe the recent development of water-splitting photocatalytic materials with a focus on metal oxide-based materials with appropriate modifications to reduce electron-hole recombination, to promote photoredox catalysis, and to utilize more visible photons.
Abstract: Photocatalytic water splitting to form H2 and O2 using illuminated semiconductors under sunlight is one of the most promising options to produce fuels from renewable resources. Numerous attempts have been made to develop photocatalysts that function under visible light irradiation to efficiently utilize solar energy. Current successful photocatalytic systems for overall water splitting can be divided into two primary approaches. One approach is to split water into H2 and O2 using a single visible-light-responsive photocatalyst with a sufficient potential to achieve overall water splitting. The other approach is to apply a two-step excitation mechanism using two different photocatalysts and a reversible electron donor/acceptor pair, which was inspired by natural photosynthesis in green plants and is called the Z-scheme. This chapter describes the recent development of water-splitting photocatalytic materials (especially in the last five years), with a focus on metal oxide-based materials with appropriate modifications to reduce electron–hole recombination, to promote photoredox catalysis, and to utilize more visible photons.
26 Sep 2016
TL;DR: In this article, a new method to modify KCa2Nb3O10 restacked nanohsheets with small Pt particle was developed, based on a simple electrostatic interaction between cationic precursor of Pt and negatively charged nanosheets.
Abstract: A new method to modify KCa2Nb3O10 restacked nanohsheets with small Pt particle was developed, based on a simple electrostatic interaction between cationic precursor of Pt and negatively charged nanosheets. Compared to an ordinary impregnation method, the location of deposited Pt particles, size and valence state were different. More concretely, Pt was deposited not only on the external surface of the restacked KCa2Nb3O10 nanohsheets, but also in the interlayer nanospace. Moreover, the deposited Pt was mainly very small (≤ 1 nm) and electron-deficient. The Pt deposited restacked KCa2Nb3O10 nanosheets showed high photocatalytic activity for overall water splitting, which is the highest one among the nanosheets-based photocatalyst. The small particle size and deposition site of Pt are possible reasons for the high activity.
01 Jan 2016
TL;DR: In this article, a review of photocatalytic CO2 reduction systems is presented, with a focus on both homogeneous and heterogeneous aspects, focusing on both heterogeneous and homogeneous aspects.
Abstract: In order to address the depletion of fossil fuels and the serious environmental problems accompanying their combustion and the concomitant CO2 emission, large-scale chemical conversion of CO2 into energy-rich materials would be an ultimate solution, and several reactions have been proposed. There have been a lot of challenges that have to be addressed in this field of research, but several breakthroughs have been achieved in recent 10 years. In this chapter, photocatalytic CO2 reduction systems, which are of particular importance, are reviewed, with a focus on both homogeneous and heterogeneous aspects.
26 Sep 2016
TL;DR: In this paper, a hybrid material consisting of a semiconductor and a binuclear metal complex having a redox photosensitizer and a catalytic unit was employed as a photocatalyst for CO2 reduction under visible light.
Abstract: A hybrid material that consists of a semiconductor and a binuclear metal complex having a redox photosensitizer and a catalytic unit was employed as a photocatalyst for CO2 reduction under visible light. It was found that this kind of hybrid was capable of reducing CO2 into HCOOH (or CO) according to two-step photoexcitation of the semiconductor and the photosensitizer unit of the metal complex. It was found that semiconductors of TaON, CaTaO2N, C3N4, and Y-Ta oxynitride became active component for this system driven by visible light (λ > 400 nm) in combination with a binuclear Ru(II) complex.
TL;DR: In this article, the photocatalytic activity was dependent on synthetic parameters such as precursor ratio and using precursor materials, post-heating conditions, which have influence on crystallinity, compositional homogeneity and the generation of Ba defects in BaTiO3:Rh, as well as the oxidation state of Rh in the material.
Abstract: Rhodium-doped barium titanate (BaTiO3:Rh) nanocrystals were prepared by hydrothermal (HT) method followed by post-heating, and examined as photocatalysts for H2 evolution from an aqueous methanol solution under visible light (λ > 420 nm). The photocatalytic activity was dependent on synthetic parameters such as precursor ratio and using precursor materials, post-heating conditions, which have influence on crystallinity, compositional homogeneity and the generation of Ba defects in BaTiO3:Rh, as well as the oxidation state of Rh in the material. Experimental results highlighted that suppressing the generation of Ba defects during the preparation process and improving the crystallinity both contributed to higher photocatalytic activity. The most active material prepared by the HT method outperformed similar analogues prepared by the polymerized complex method and a conventional solid state reaction method.